Hand held devices are now becoming a hub for personal communication and individual mobile computing needs. It is a centre for the convergence of multiple media types and multiple networking standards that are best suited to transport a specific types of data.
BLUETOOTH (IEEE-802.15.1 Industry Standard) and wireless local area network (WLAN) networking (IEEE-802.11 a/b/g Industry Standards) have been used extensively in hand-held personal communication devices. A Packet Traffic Arbitration (PTA) algorithm for time division multiple access (TDMA) has been used quiet successfully to allow two networks, such as WLAN and BLUETOOTH, to be collocated with sufficient throughput on both to support useful communication.
But the throughput requirements of such networks has been expanding in step with market needs. The throughput increases on each of the networks, means increased wireless medium traffic reservation periods, e.g., IEEE-802.11n for WLAN, and Extended Data Rate (EDR) extensions for BLUETOOTH.
The PTA algorithm relies heavily on there being enough quite time in both networks to deliver whole frames without errors. However, the frequency and duration of quiet periods is reduced in advanced IEEE-802.11n networks. So, it becomes necessary for each network to recognize the medium reservation requirements of the other collocated network.
Typically, the PTA algorithm uses hardware signaling methods to reserve the medium, either for WLAN or BLUETOOTH traffic. Such reservation scheme presupposes that the WLAN Station will have a sufficient number and duration of quiet periods to allow asynchronous and isochronous BLUETOOTH traffic.
However, new standards like the IEEE-802.11n allow aggregated frame transfers of MAC service and protocol data units. Such can result in a serious depletion of the number of available WLAN quiet periods. The WLAN medium access windows can be as long as a few milliseconds, especially with hand-held devices that operate at under 100 Mbps/second transfer rates.
BLUETOOTH isochronous transfers need quiet periods that are at least 2.5 milliseconds long. It is getting increasingly more difficult in newer devices to accommodate the error-free transfer of IEEE-802.11n frames while still supporting BLUETOOTH traffic. The errors caused by the collision of needs to access the medium results in a larger number of retrials and corresponding inefficiencies.
Some background in WLAN IEEE-802.11 developments would be helpful in understanding the present invention. Tim Godfrey, Globespan Virata, in a COMMSDESIGN article dated Dec. 19, 2003, explains that a hybrid coordination function (HCF) in the IEEE-802.11e Standard replaces the IEEE-802.11-legacy distributed coordination function (DCF) and point coordination function (PCF) in a quality of service (QoS) station (QSTA), as discussed at the commdesign website. The HCF includes two access mechanisms, an enhanced distributed channel access (EDCA), and an HCF controlled channel access (HCCA). The HCF defines a uniform set of frame exchange sequences that are usable at any time, and allocates rights to transmit with transmit opportunities (TXOPs) granted to QSTA's through the channel access mechanisms. Each TXOP grants a particular QSTA the right to use the medium at a defined point in time, and for a defined maximum duration. The allowed duration of TXOP's are communicated globally in the EDCA station beacon.
The HCF introduced new acknowledgement (ACK) rules. Before, every unicast data frame required an immediate response with an ACK control frame. Now, HCF allows either no-acknowledgement, or block-acknowledgement, and which to use is specified in a QoS data frame control field. The no-acknowledgement is useful in applications with very low jitter tolerance, e.g., streaming multimedia, where retry delays would make the data unusable. Block-acknowledgements can increase efficiency by aggregating the ACK's for multiple received frames into a single response.
In EDCA, the contention window and backoff times are adjusted to favor higher priority classes gaining medium access. Eight user priority levels are available, and each priority is mapped to an “Access Category”, which corresponds to one of four transmit queues. Each queue provides frames to an independent channel access function, each of which implements the EDCA contention algorithm. When frames are available in multiple transmit queues, contention for the medium occurs both internally and externally, based on the same coordination function. The internal scheduling resembles the external scheduling. Internal collisions are resolved by allowing frames with the higher priority to transmit, while the lower priority frames are subjected to a queue-specific backoff as if a collision had occurred.
The minimum idle delay before contention, the minimum and maximum contention windows, and other parameters defining EDCA operation are stored locally by the QSTA. Such parameters can be different for each access category (queue), and can be individually updated for each access category by a QoS access point (QAP) through the EDCA parameter sets. The parameters are sent from the QAP as part of the beacon, and in probe and re-association response frames. The stations in the network can then be adjusted to changing conditions, and the QAP can manage the overall QoS.
Under EDCA, stations and access points use the same access mechanism and contend on an equal basis at a given priority. A station that wins an EDCA contention is granted a transmit opportunity (TXOP), the right to use the medium for a period of time. The duration of each TXOP is specified per access category, and is included in the TXOP limit field of the access category (AC) parameter record in the EDCA parameter set. A QSTA can use a TXOP to transmit multiple frames within an access category.
If a frame exchange sequence has been completed, and there is still time remaining in the TXOP, the QSTA can extend the frame exchange sequence by transmitting another frame in the same access category. The QSTA must ensure that the transmitted frame and any necessary acknowledgement can fit into the time remaining in the TXOP.
The IEEE-802.11-type contention-based medium access is susceptible to severe performance degradation when overloaded. In overload conditions, the contention windows become large, and more and more time is spent in backoff delays rather than sending data. Admission control in the IEEE-802.11e networks regulates the amount of data contending for the medium.
IEEE-802.11e is an enhancement of the IEEE-802.11a and IEEE-802.11b wireless LAN (WLAN) specifications. It offers quality of service (QoS) features, including the prioritization of data, voice, and video transmissions. The IEEE-802.11a, IEEE-802.11b, and IEEE-802.11e standards are elements of the IEEE-802.11 family of specifications for wireless local area networks.
IEEE-802.11e enhances the IEEE-802.11 Media Access Control layer (MAC layer) with a coordinated time division multiple access (TDMA) construct, and adds error-correcting mechanisms for delay-sensitive applications such as voice and video. The IEEE-802.11e specification enables seamless interoperability and is especially well suited for use in networks that include multimedia capability. It supports high-speed Internet access with full-motion video, high-fidelity audio, and Voice over IP (VoIP).
IEEE-802.11e networks operate in two ranges, 2.400-2.4835 GHz (the same as IEEE-802.11b networks), or 5.725 GHz to 5.850 GHz (the same as IEEE-802.11a networks). There are certain advantages to the higher frequency range, including faster data transfer speed, more channels, and reduced susceptibility to interference.
The four basic parts of a BLUETOOTH system are a radio frequency (RF) unit, a baseband or link control unit, link management software, and the supporting application software.
The BLUETOOTH radio is a short-distance, low-power radio operating in the unlicensed spectrum of 2.4-gigahertz (GHz). The radio uses a nominal antenna power of 0-dBm (1-mW) and has a range of 10 meters. Optionally, a range of 100 meters may be achieved by using an antenna power of 20-dBm (100-mW). Data is transmitted at a maximum rate of one megabit per second. However, communication protocol overhead limits the practical data rate to about 721-Kbps.
BLUETOOTH uses spectrum spreading, the transmission hops among seventy-nine different frequencies between 2.402-GHz and 2.480-GHz at nominal rate of 1600-hops/s. Spectrum spreading minimizes interference from other devices in the 2.4-GHz band, such other wireless networks. If a transmission encounters interference, it waits 625-microseconds for the next frequency hop and retransmits on a new frequency. Frequency hopping also provides data security because two packets of data are never sent consecutively over the same frequency, and the changing frequencies are pseudo-random.
The link controller handles all the BLUETOOTH baseband functions, e.g., encoding voice and data packets, error correction, slot delimitation, frequency hopping, radio interface, data encryption, and link authentication. It also executes the link management software.
The IEEE-802.11e Standard defines a hybrid coordination function (HCF) used in the quality of service (QoS) enhance basic service set (QBSS). The HCF has two modes of operation, enhanced distributed channel access (EDCA) and HCF controlled channel access (HCCA). EDCA can support prioritized traffic. EDCA is a contention-based channel access function, and HCCA is based on a polling mechanism, controlled by a hybrid coordinator (HC). The HC is co-located with the QoS enhanced access point (QAP). Both access functions enhance or extend functionality of the original IEEE-802.11 DCF and PCF access methods.
Two other elements introduced by the IEEE IEEE-802.11e MAC are the access category (AC) and transmission opportunity (TXOP) in the HCF. The TXOP reserves an interval of time when a particular QoS enhanced client station (QSTA) has the right to make frame exchanges over the wireless medium. The TXOP can be obtained using the contention-based channel access, e.g., an enhanced distributed access channel (EDCA) TXOP. The EDCA-TXOP is announced in the beacon frame transmitted by the QoS enhanced access point (QAP). The QSTA's each contend for EDCA TXOP. The TXOP can also be granted by HCF controlled channel access (HCCA), it is a HCCA (polled) TXOP. The HCCA channel access method TXOP is included in the QoS poll frame transmitted to a QSTA by the QAP when it polls the QSTA to start frame transmission. Once a QSTA gets the medium access right, it is allowed to transmit multiple frames during its exclusive time slot.
Each station using the EDCA has four AC's, each with one transmit queue with an independent mechanism to contend for medium access. The four AC's have different priorities, and are intended for different kinds of traffic, e.g., background (AC BK), best effort (AC BE), video (AC VI), and voice (AC VO). The TXOP defines the starting time and maximum duration that a station may transmit frames.
In the IEEE IEEE-802.11e Standard, when a QSTA has a traffic stream (TS) such as an audio-video (AV) stream to transmit, it sends an add TS (ADDTS) request to QAP to ask for transmission permission for the TS before starting transmission. Such ADDTS request includes a traffic specification (TSPEC) which specifies the characteristics and QoS expectations of the TS, e.g., TS ID, data rate, data unit size, desired PHY rate, medium access method (EDCA or HCCA), etc. When the QAP receives the ADDTS request, it will evaluate the request in view of the TSPEC element, available bandwidth, channel condition, network loading, etc. If the bandwidth is available, the QAP will accept the request. The QAP transmits its decision with an ADDTS response to the requesting QSTA. If the request is accepted the QSTA shall start transmitting the TS. Otherwise, the QSTA shall not transmit the TS.
Each AC has its own transmit queue and its own set of AC parameters. The differentiation in priority between AC is realized by setting different values for the AC parameters. The most important of which are, Arbitrary inter-frame space number (AIFSN). The minimum time interval between the wireless medium becoming idle and the start of transmission of a frame; Contention Window (CW), A random number is drawn from this interval, or window, for the backoff mechanism; and, TXOP Limit, The maximum duration for which a QSTA can transmit after obtaining a TXOP. When data arrives at the MAC-UNITDATA service access point (SAP), the IEEE-802.11e MAC first classifies the data with the appropriate AC, and then pushes the newly arrived MSDU into the appropriate AC transmit queue. MSDUs from different ACs contend for EDCA-TXOP internally within the QSTA. The internal contention algorithm calculates the backoff, independently for each AC, based on AIFSN, contention window, and a random number. The backoff procedure is similar to that in DCF, and the AC with the smallest backoff wins the internal contention. The winning AC would then contend externally for the wireless medium. The external contention algorithm has not changed significantly compared to DCF, except that in DCF the deferral and backoff were constant for a particular PHY. IEEE-802.11e has changed the deferral and backoff to be variable, and the values are set according to the appropriate AC. With proper tuning of AC parameters, traffic performance from different ACs can be optimized and prioritization of traffic can be achieved. This requires a central coordinator (QAP) to maintain a common set of AC parameters to guarantee fairness of access for all QSTA within the QBSS. Also in order to address the asymmetry between uplink (QSTA to QAP) and the much heavier downlink (QAP to QSTA) traffic, a separate set of EDCA parameters is defined for the QAP only, which takes this asymmetry into account.
The traffic specification (TSPEC) is the traffic stream management device provides the management link between higher layer QoS protocols such as IntServ or DiffServ with the IEEE-802.11e channel access functions. TSPEC describes data rate, packet size, delay, and service interval. TSPEC negotiation between peer MAC layers provides the mechanism for controlling admission, establishment, adjustment and removal of traffic streams. Traffic stream admission control is especially important since there is limited bandwidth available in the wireless medium. Bandwidth access must be controlled to avoid traffic congestion, which can lead to breaking established QoS and drastic degradation of overall throughput. The IEEE-802.11e standard specifies the use of Traffic Specification (TSPEC) for such a purpose for both EDCA and HCCA.
QoS management frames, primitives, and procedures are defined for TSPEC negotiation, which is always initiated by the station management entity (SME) of a QSTA, and accepted or rejected by the HC. Requested TSPEC is communicated to the MAC via the MAC layer management entity (MLME) SAP. This allows higher layer SW, protocols, and application, such as RSVP, to allocate resources within the MAC layer.
Admission control is negotiated by the use of a TSPEC. A station specifies its traffic flow requirements (data rate, delay bounds, packet size, and others) and requests the QAP to create a TSPEC by sending the ADDTS (add TSPEC) management action frame. The QAP calculates the existing load based on the current set of issued TSPECs. Based on the current conditions, the QAP may accept or deny the new TSPEC request. If the TSPEC is denied, the high priority access category inside the QSTA is not permitted to use the high priority access parameters, but it must use lower priority parameters instead. Admission control is not intended to be used for the “best effort” and “background” traffic classes.
What is needed is a system that allows WLAN client stations (STA's) to recognize and declare the needs of BLUETOOTH traffic as one of the supported traffic streams to the Access Point of the WLAN network, and thus reserve medium time for BLUETOOTH traffic.